A rotary fluid machine disclosed in Japanese Patent Application Laid-open No. 2000-320543 is equipped with a vane piston unit in which a vane and a piston are combined; the piston, which is slidably fitted in a cylinder provided radially in a rotor, interconverts the pressure energy of a gas-phase working medium and the rotational energy of the rotor via a power conversion device comprising an annular channel and a roller, and the vane, which is radially and slidably supported in the rotor, interconverts the pressure energy of the gas-phase working medium and the rotational energy of the rotor.
In such a rotary fluid machine, a rotating shaft, which is fixed to the rotor, is rotatably supported on a fixed shaft, which is fixed to a casing; a hydrostatic bearing is formed by supplying a liquid-phase working medium to sliding surfaces of the fixed shaft and the rotating shaft, and a hydrostatic bearing is also formed by supplying the liquid-phase working medium to sliding surfaces of the vane and a vane channel. Since the pressures of the liquid-phase working medium that are required for the hydrostatic bearings are different from each other, if high pressure water is supplied to the two hydrostatic bearings so as to suit the hydrostatic bearing that requires a high pressure, there is the problem that leakage of the liquid-phase working medium increases wastefully in the hydrostatic bearing that requires a low pressure, and if low pressure water is supplied to the two hydrostatic bearings so as to suit the hydrostatic bearing that requires a low pressure, there is the problem that a sufficient lubrication function cannot be exhibited in the hydrostatic bearing that requires a high pressure.